Bizarre self-assembling quasicrystals accidentally created in lab

Quasicrystals have teased and intrigued scientists for three
decades. Now, this already strange group of materials has a bizarre
new member: a two-dimensional quasicrystal made from
self-assembling organic molecules.

This odd quasicrystal is flat, made from a single layer of
molecules with five-sided rings. The molecules form groups within
the layer as weak hydrogen bonds link them together. These
molecular groups are assembled in a way that forces other molecules
in the layer into shapes including pentagons, stars, boats, and
rhombi. If this were a regular old crystal, you'd expect to see
these groups and shapes repeated over and over throughout the layer
in a predictable way. But in this quasicrystal, you'll see the same
shapes over and over in the layer, but not in any organised
pattern.

The things that set these quasicrystals apart from all the
others, scientists say, are its organic materials and
self-assembling parts.

"They're markedly different from just about everything else out
there," said physical chemist Alex
Kandel, whose lab at the University of Notre Dame described the
material today in Nature. Previously known
quasicrystals are mostly metallic, and tied together by strong
ionic bonds rather than the weaker hydrogen bonds that can be found
in complex organic molecules like DNA.

As their name suggests, quasicrystals have a structure that's
part crystalline, part disorganised. In other words, they are
something in between a structure with repeating, symmetric
units, and one with completely random building blocks. Their
atomic units are locally symmetric, but are not regularly repeated
over longer distances. Because of these arrangements, quasicrystals
are slippery and have been used in things like non-stick frying pans.

The first quasicrystal of any sort was also accidentally made in
the lab, in 1982, by materials scientist Daniel Schechtman who won a Nobel Prize for the discovery in 2011. Up until that
point, scientists thought the semi-organised structure of
quasicrystals was an impossibility. Now, we know that's not true.
Not only can quasicrystals be grown in the lab, they can also grow
in nature. In 2012, Princeton University physicist Paul
Steinhardt showed that quasicrystals found in eastern
Russia had fallen to Earth in a meteorite.

Kandel's group discovered the organic quasicrystal accidentally.
Instead of trying to make the thing, they were actually hoping to
study how electrons are distributed in ferrocenecarboxylic acid,
the molecule the quasicrystal is built from. To do that, the team
needed to build a stable, linear group of molecules. But when the
scientists tried, they produced a two-dimensional quasicrystal
instead.

"The first images were quite a shock," Kandel said. "Certainly,
2D quasicrystals aren't easy to make, which is why we're only
seeing very recent reports of them now, some 30-odd years after the
first quasicrystalline materials were discovered."

Wolf Widdra of Germany's Martin Luther University, who made
the first 2D quasicrystal, reported in October 2013, is a bit skeptical of the new
research. He doesn't think there's enough evidence yet to
prove quasicrystal structure over a large enough area.

There is also disagreement among scientists about what it means
to be self-assembling. Widdra thinks the term could be applied
to all quasicrystal structures, not just this new one. Kandel
argues that structures assembled by way of strong chemical bonds --
like the other quasicrystals -- aren't actually self-assembled.
Those strong chemical bonds, he says, overwhelm the forces holding
individual building blocks together and leave the material no
choice but to form. In this new quasicrystal, those building blocks
are joined by weak hydrogen bonds.

"Self-assembly is interesting precisely because the forces that
drive organisation are weaker than the forces responsible for the
individual structure," Kandel said.